The White House has said it is 'still hopeful' that a planned summit between North Korean leader Kim Jong Un and U.S. President Donald Trump will go ahead, despite Pyongyang's threat to cancel the historic event.

'We're still hopeful that the meeting will take place and we'll continue down that path,' White House spokeswoman Sarah Sanders said in an interview with Fox News on May 16. 'At the same time...we've been prepared that these might be tough negotiations.'

'The president is ready if the meeting takes place. And if it doesn't, we will continue the maximum pressure campaign that has been ongoing,' Sanders said.

Sanders was speaking after the North suspended high-level talks with the South scheduled for May 16 over joint U.S.-South Korean military exercises, and also cast doubt on whether the summit could go ahead as planned on June 12 in Singapore.

'The United States will also have to undertake careful deliberations about the fate of the planned North Korea-U.S. summit,' South Korea's Yonhap news agency quoted the North's official KCNA news agency as saying.

KCNA also described the U.S.-South Korean drills as a 'provocation running counter to the positive political development on the Korean Peninsula.'

North Korean first vice foreign minister Kim Kye Gwan said hours later, 'we are no longer interested in a negotiation that will be all about...making a one-sided demand for us to give up our nukes.'

Some 100 warplanes, including B-52 bombers and F-15K fighters began the two-week Max Thunder drills on May 11.

The United States and South Korea say such exercises are for defensive purposes only.